Analysis of component criticality in the blowout preventer

(1)

Page | i Faculty of Science and Technology

MASTER’S THESIS

Study program/ Specialization:

Offshore Technology/ Risk Management

Spring semester, 2012

Open / Restricted access Writer:

Yahya Januarilham

………

(Writer’s signature)

Faculty supervisor:

Terje Aven

External supervisor(s):

Thomas Black Fylking (Scandpower AS) Louise Bengtsson (Scandpower AS) Title of thesis:

Analysis of Component Criticality in the Blowout Preventer

Credits (ECTS): 30 ECTS Key words:

Blowout Preventer Criticality

FMECA Kick Reliability

Pages : 92

+ enclosure : 44

Stavanger, 15.06.2012 Date/year

(2)

Page | ii

ABSTRACT

During well drilling operation, there is a possibility of a kick (influx). When a kick is not controlled properly it will become a blow out. This is an uncontrolled and sudden flow of formation fluid that releases from a reservoir through a well bore into surface as a result of pressure difference in formation and well. The kick could flow to surface and create explosions causing fatality, environment damage and loss of asset resulting in high cost.

There are procedures and methods to deal with the occurrence of kicks and blowouts in order to control a well flow. Moreover, well barriers should be established and designed based on the characteristics of the reservoir and rock formation. The last line of protection in well barriers is known as Blowout Preventer (BOP). It is one of the most important barriers to prevent unintentional hydrocarbon release when all well barriers in a well have failed. There are many factors that influence the performance of a BOP. The purpose of this thesis is to determine the criticality of components in BOP related to the redundancies they have during well shut in, stripping, snubbing and BOP testing operation. By knowing the criticality of BOP components, we can assure which components that should be focused on for maintenance and testing. It will also indicate which components that gives redundancy to the BOP during well shut in, stripping, snubbing and BOP testing operation, if one or more components are failed. A literature study is the main work of this thesis. Studying the principal, functions, operations and factors related to drilling activity with respect to the use of BOP. In addition, relevant regulations and standards are also describes to specify the required specification of BOP. The analysis of criticality is done by using risk tools such as reliability block diagram, FMECA, criticality matrix, redundancy and effect table. All of these risk tools complement each other to give the final conclusion of critical component in a BOP. The result of the analysis shows five critical components in a BOP with the prioritization start from shuttle valve (blind shear ram function), blind shear ram (ram piston), flange (BOP stack), gasket (BOP stack) and annular preventer (rubber housing) respectively. In the event of kick and well shut in is initiated, the above critical component is very critical to the safety of personnel.

Stripping and snubbing operation also require the critical components to be function properly, but with less critical when well shut in has been done earlier. During BOP testing operation, the critical components might not be critical if it fail as there are many safety measure and procedure for safety.

(3)

Page | iii

ACKNOWLEDGMENT

Praise and gratitude I prayed to God Almighty for His blessings so I can finish the thesis report. The thesis report is done in order to meet one of the requirements to achieve Master of Science (M.Sc) degree in Offshore Technology, Risk Management specialization from the University of Stavanger. I realize that without the help and guidance from various parties, it would be very difficult for me to finish the thesis report. Thus, I would like to thank to:

1. My supervisor at UiS, Prof. Terje Aven, who has provided his time, idea and advice to guide me in the writing and preparation of the thesis

2. My supervisor at Scandpower, Thomas Black Fylking and Louise Bengtsson, for providing their time to guide me in the construction of the thesis in general and the analysis part of the thesis

3. My parents and sisters who have provided material assistance and moral support in the completion of the thesis

4. My friends and colleagues at UiS and Scandpower who gave me supports

I hope that God Almighty is pleased to reply to all the good of those who have helped.

Hopefully this project can bring benefits to the development of science.

Stavanger, June 2012

Yahya Januarilham

(4)

Page | iv

TABLE OF CONTENT

LIST OF FIGURES

FIGURE 1.1BARRIER FAILURES IN THE DEEPWATER MACONDO ACCIDENT (BPINVESTIGATION TEAM,2010) ... 1

FIGURE 2.1THE IMPORTANT PARTS OF THE DRILLING RIG (STONELEY,R.,1995) ... 4

FIGURE 2.2COMPLETION BY USING LANDING STRING SYSTEMS FOR RUNNING IN MARINE RISER (SUBSEA1,2010) ... 6

FIGURE 2.3SURFACE AND SUBSEA TREE (ODLAND,J.,2010) ... 6

FIGURE 2.4UNDERGROUND BLOWOUTS FROM A WELL REACH SURFACE (CHU,D.,L.,2010) ... 8

FIGURE 2.5LOSS OF STABILITY IN SHALLOW GAS KICK (RIG TRAIN,2001) ... 11

FIGURE 3.1U-TUBE MODEL OF THE BOTTOM HOLE PRESSURE (GRACE,R.,D.,2003) ... 15

FIGURE 3.2FLOW CHART OF KICK CONTROL PROCEDURE (SCHLUMBERGER,2012) ... 17

FIGURE 4.1TYPICAL MAIN COMPONENTS IN SUBSEA BOP AND LMRP(SUBSEA1,2010)(TRANSOCEAN,2011) ... 18

FIGURE 4.2EXAMPLE OF CUTAWAY VIEW OF BLOWOUT PREVENTER STACK COMPONENTS (TRANSOCEAN,2011) ... 19

FIGURE 4.3BLOWOUT PREVENTER STACK WITH PREVENTER AND RAMS CLOSE (GOINS,W.,C.,SHEFFIELD,R.,1983) ... 21

FIGURE 4.4TYPICAL SUBSEA BOP STACK (REES,A.,DANIEL,M.,2011)... 22

FIGURE 4.5TYPICAL KILL AND CHOKE LINES CONFIGURATION (GOINS,W.,C.,SHEFFIELD,R.,1983) ... 22

FIGURE 4.6SEALING ELEMENT AND STEEL REINFORCEMENT SEGMENTS IN AN ANNULAR PREVENTER (VUJASINOVIC,A.,1986) ... 24

FIGURE 4.7SHAFFER SPHERICAL BOP(RIG TRAIN,2001) ... 24

FIGURE 4.8THE CLOSING OF SHAFFER SPHERICAL BOP(RIG TRAIN,2001) ... 24

FIGURE 4.9DLANNULAR BLOWOUT PREVENTER (RIG TRAIN,2001) ... 25

FIGURE 4.10PACKING ELEMENT COMPONENTS AND OPERATIONS (RIG TRAIN,2001) ... 25

FIGURE 4.11ANNULAR HYDRIL GK TYPE (RIG TRAIN,2001) ... 26

FIGURE 4.12ANNULAR HYDRIL GL TYPE (RIG TRAIN,2001) ... 26

FIGURE 4.13TYPICAL PIPE/CASING RAMS (RIG TRAIN,2001) ... 27

FIGURE 4.14TYPICAL BLIND/SHEAR RAM (TRANSOCEAN,2011) ... 27

FIGURE 4.15TYPICAL VARIABLE BORE RAMS (RIG TRAIN,2001)(TRANSOCEAN,2011) ... 28

FIGURE 4.16TYPICAL FLEX PACKER (RIG TRAIN,2001) ... 28

FIGURE 4.17TYPICAL DUAL BORE FLEX PACKER (RIG TRAIN,2001) ... 28

FIGURE 4.18BLIND SHEAR RAMS CLOSING (GRÖNDAHL,M., ET AL.,2010)(RIG TRAIN,2001) ... 29

FIGURE 4.19BOP CONTROL SYSTEM IN MACONDO DEEPWATER HORIZON (GRÖNDAHL,M., ET AL.,2010) ... 31

FIGURE 4.20TYPICAL ELECTRO HYDRAULIC CABLE (TOP LEFT),MUX CABLE (TOP RIGHT) AND HYDRAULIC HOSE (BOTTOM)(GOINS, W.,C.,SHEFFIELD,R.,1983)(UMBILICALS,2009)(RIG TRAIN,2001) ... 32

FIGURE 4.21EXAMPLE OF REDUNDANCY BETWEEN PODS AND STACK (RIG TRAIN,2001) ... 33

FIGURE 4.22GENERAL ARRANGMENT OF HYDRAULIC SUBSEA BOP CONTROL SYSTEM (RIG TRAIN,2001) ... 35

FIGURE 4.23SCHEMATIC OF BLOCK FUNCTION FOR SUBSEA BOP CONTROL SYSTEM (RIG TRAIN,2001) ... 36

FIGURE 4.24SCHEMATIC OF OPEN FUNCTION FOR SUBSEA BOP CONTROL SYSTEM (RIG TRAIN,2001) ... 37

FIGURE 4.25SCHEMATIC OF CLOSE FUNCTION FOR SUBSEA BOP CONTROL SYSTEM (RIG TRAIN,2001) ... 38

FIGURE 4.26SCHEMATIC FLOWS OF CONTROL FLUID CIRCUIT AND ACCUMULATOR RECHARGE SYSTEM (RIG TRAIN,2001) ... 40

FIGURE 4.27SCHEMATIC FLOWS OF PILOT FLUID CIRCUIT (RIG TRAIN,2001) ... 42

FIGURE 5.1SUBSEA BOP STACK ARRANGEMENT (SEDCO FOREX,1999) ... 43

FIGURE 6.0.1TESTING BLIND RAM (GOINS,W.,C.,SHEFFIELD,R.,1983) ... 54

FIGURE 6.0.2TESTING PIPE RAMS, ANNULAR AND ALL CHOKE AND KILL MANIFOLDS, FLOWLINES AND BOP WING VALVES (GOINS, W.,C.,SHEFFIELD,R.,1983) ... 55

FIGURE 7.1STEP TO DETERMINE APPROPRIATE RISK ASSESSMENT (HSE,2006) ... 56

FIGURE 7.2EXAMPLE OF RELIABILITY BLOCK DIAGRAM OF BOP ACTIVATION (TUMER,I., ET AL.,2010) ... 58

FIGURE 7.3FLOWCHART OF FMECA(IEC60812,2006) ... 60

FIGURE 7.4CRITICALITY MATRIX ... 65

FIGURE 8.1RELIABILITY BLOCK DIAGRAM FOR BOP RAMS CLOSE FUNCTION ... 71

FIGURE 8.2RELIABILITY BLOCK DIAGRAM FOR CONTROL FLUID CIRCUIT AND SUBSEA ACCUMULATOR RECHARGE SYSTEM ... 73

FIGURE 8.3RELIABILITY BLOCK DIAGRAM FOR ANNULAR PREVENTER CLOSE AND OPEN FUNCTION ... 75

FIGURE 8.4RELIABILITY BLOCK DIAGRAM FOR RAM PREVENTER ... 75

FIGURE 8.5CRITICALITY MATRIX FOR BOP CONTROL SYSTEM FAILURE MODES ... 78

FIGURE 12.1WELL BARRIER SCHEMATIC FOR RUNNING NON-SHEARABLE DRILL STRING (LEFT) AND DRILLING, CORING AND TRIPPING WITH SHEARABLE DRILL STRING (RIGHT)(NORSOK D-010,2004) ... 124

FIGURE 12.2WELL BARRIER SCHEMATIC FOR RUNNING NON-SHEARABLE CASING (LEFT) AND DRILLING THROUGH TUBING DRILLING AND CORING (RIGHT)(NORSOK D-010,2004) ... 125

FIGURE 12.3CASINGS INSIDE WELLBORE (SCHLUMBERGER,2012) ... 127

FIGURE 12.4FLOW OF DIVERTED GAS (LEFT) AND SCHEMATIC OF TYPICAL INSTALLATION FOR FLOATING DRILLING PLATFORM (RIGHT) (RIG TRAIN,2010)(HAWKER,2001)... 130

(7)

Page | vii

FIGURE 12.5 HAFFER ROTATING HEAD AND STRIPPER (GOINS,W.,C.,SHEFFIELD,R.,1983) ... 131

FIGURE 12.6SOME TYPE OF FLEX JOINT (OIL STATES,2012) ... 132

FIGURE 12.7WELLHEAD CONNECTOR AND ITS CONNECTION SEQUENCE (RADOIL,2009) ... 132

FIGURE 12.8PRESSURES ACTED IN A WELLBORE (HAWKER,D.,2001) ... 133

FIGURE 12.9RELATIONSHIP BETWEEN DEPTH AND PRESSURE FOR DIFFERENT PRESSURES ACTING IN A WELLBORE (HAWKER,D.,2001) ... 134

(8)

Page | viii

LIST OF TABLES

TABLE 2.1INDICATORS OF THE OCCURRENCE POSSIBILITY OF KICKS (HAWKER,D.,2001)... 12

TABLE 2.2INDICATORS OF THE OCCURRENCE POSSIBILITY OF KICKS (GOINS,W.,C.,SHEFFIELD,R.,1983) ... 12

TABLE 6.1SHUT IN PROCEDURES (WELL CONTROL SCHOOL,2004) ... 47

TABLE 7.1 FIGURE AND FORMULA OF SERIES AND PARALLEL STRUCTURE IN RBD ... 58

TABLE 7.2FAILURE PROBABILITY RANK ... 64

TABLE 7.3EFFECT SEVERITY RANK ... 64

TABLE 7.4PROS AND CONS OF FMECA ... 67

TABLE 8.1OPERATION MODES OF COMPONENTS FOR DIFFERENT BOP FUNCTIONS ... 72

TABLE 8.2LISTS OF COMPONENTS AND THE CORRESPONDING FAILURE MODES ... 76

TABLE 8.4PRIORITIZATION OF BOP COMPONENT CRITICALITY FROM CRITICALITY MATRIX ... 78

TABLE 8.5REDUNDANCY AND EFFECT TABLE OF SUBSEA BOP ... 79

TABLE 8.6SUMMARY OF CRITICAL COMPONENT FROM REDUNDANCY AND EFFECT TABLE ... 83

TABLE 9.1LIST OF CRITICAL COMPONENTS BASED ON THE USED RISK TOOLS ... 84

TABLE 12.1FMECA OF HYDRAULIC BOP SYSTEM ... 93

(9)

Page | ix

TERMINOLOGY

Annulus The space between two concentric objects, such as between the wellbore and casing or between casing and tubing, where fluid can flow (Schlumberger, 2012)

Blow out A flow of formation fluids into the wellbore that cannot be controlled at surface (Schlumberger, 2012)

Bell Nipple A pipe located on the top of a casing string that provides guidance for drilling tools into the hole .It is also called mud riser or flow stack (Schlumberger, 2012) (Goins, W., C., Sheffield, R., 1983)

Blow Out Preventer A structure with a large set of valves and rams placed on the top of the well that can be closed when the drilling crew have uncontrolled flow of formation fluids (Subsea1, 2010)

Burst Pressure The differential internal pressure where a joint of casing will fail. It is a key consideration for well control and contingency operation as well as an indicator in the well design process (Schlumberger, 2012)

Casing Steel pipe used to protect the wall of the well after drilling to prevent it from collapsing and prevent the fluid in the rocks to enter the well bore. (Stoneley, R., 1995)

Caving Rocks fragments that come from the well bore but not necessarily come from the drill bit cuttings nor drilling fluid flow (Schlumberger, 2012). It could the fragments from the broken weak or impermeable rock formations.

Completion Assembly of down hole tubulars and equipments required to enable safe and efficient production from an oil and gas well (Odland, J., 2010)

Connection Gas A short entry of gas into drilling fluid in the drilling operation during pipe connection as a result of mud pumping stoppage which allows gas to enter the wellbore. It is also occur as a result of swabbing effects from the drill string movement during connection (Schlumberger, 2012)

Cut set A set of events/components in a system whose occurrence (at the same time) ensures the system to fail (Rausand, M., Høyland A., 2004)

Differential Sticking A situation where the drill string is stick into the well bore/bore hole embedded by mud cake or filter cake and cannot be rotated (Schlumberger, 2012)

Draw Works A large horizontal hoist carrying cable on the drilling rig used to raise and lower the drill string (Stoneley, R., 1995)

Drill Bit The tool used to crush or cut rock. It works by scraping or crushing or both, usually as part of a rotational motion (Schlumberger, 2012) Drill Break A change in the rate of drilling penetration as a result of drilling into a

different rock formation such as from shale into limestone (Malhotra, S., M., 2005)

Drill Collars Tube that is used between drill pipe and bit in the drill string to provide additional weight on the bit and give more pendulum effect to the drill string (Malhotra, S., M., 2005)

(10)

Page | x Drill Stem Test A test to determine the productive capacity, pressure and permeability

of a hydrocarbon reservoir (Schlumberger, 2012)

Drill String The steel pipe where the drill bit is attached on the bottom and which is rotated in the well during drilling. It consists of section(s) with a length of 30 ft (Stoneley, R., 1995)

Drilling Fluid/Mud A fluid that is used in drilling operation that contains solid suspensions, mixtures and emulsions of liquid, gases and solids (Schlumberger, 2012)

Emergency Disconnect A package which enables quick disconnection between marine riser Package and blow out preventer (BOP) in case of emergency (Subsea1, 2010) Equivalent Mud Weight specific weight of drilling mud that is exerted to hold the pressure of

the formation fluid in the equivalent value (SPE E&P, 2011)

Flowing Well A well that has enough natural pressure from reservoirs to flow oil without the aid of pump (Schlumberger, 2012)

Gas-Cut Mud A drilling fluid that is contaminated by gas causing reduction in its density (Schlumberger, 2012)

Hydrostatic Pressure The pressure exerted by a fluid at rest. It increases along with the density and depth of the fluid and is expressed in pounds per square inch (psi) (Malhotra, S., M., 2005)

Kelly The top section of the drill string, square or hexagonal in cross section. It is used to transmit rotary motion from the rotary table or kelly bushing to the drillstring, while allowing the drill string to be lowered or raised during rotation (Schlumberger, 2012)

Kelly Bushing An adapter to connect the rotary table to the kelly (Schlumberger, 2012)

Kick An incoming flow of formation fluid into the wellbore that can be controlled at surface (Hawker, D., 2001)

Kill Stop the flow of fluid inside the wellbore by circulating higher mud weight to balance the pressure in the well when influx (kick) occur (Schlumberger, 2012)

Landing String A tool to facilitates well control during completion and workover operations (Subsea1, 2010)

Log (Logging) The examination of one or more physical characteristics in or around a well against the depth or time or both (Schlumberger, 2012)

Lower Marine Riser Package A package that makes a quick disconnection between marine riser and blow out preventer (BOP) in case of emergency (Subsea1, 2010) Lower Riser Package A package which enables well control in case of emergency

(Subsea1, 2010)

Marine Riser A pipe connection between drilling platform and Blowout Preventer (BOP) on the seafloor (Subsea1, 2010)

Minimum cut set A cut set that cannot be reduced without losing its status as a cut set (Rausand, M., Høyland A., 2004)

Minimum path set A path set that cannot be reduced without losing its status as a path set (Rausand, M., Høyland A., 2004)

(11)

Page | xi Nipple Part of a pipe which have threaded section at both ends with male

threads (Schlumberger, 2012)

Open Hole Parts of a well that are not protected with casing (Schlumberger, 2012)

Path set A set of events/components in a system whose occurrence (at the same time) ensures the system to function (Rausand, M., Høyland A., 2004)

Pay/Pay Zone A reservoir or portion of a reservoir which contains economically producible hydrocarbons (Schlumberger, 2012)

Perforation The path or channel in the final casing or liner that gives communication into the reservoir formation where hydrocarbon is produced (Schlumberger, 2012)

Rate of Penetration A rate of how fast the bit drills into formations, usually expressed in feet or meters per hour or minutes per foot (meter) (Malhotra, S., M., 2005)

Rotary Table The rotating part of the drill floor that supplies power to rotate the drill string in a clockwise direction (Schlumberger, 2012)

Shut In Sealing a well to protect against kick by closing BOP and chokes (Malhotra, S., M., 2005)

Slips A device used to grip and suspend the drill string on the rotary table (Schlumberger, 2012)

Snubbing The process of placing drill pipe into the well bore by pushing it down when the BOPs are closed and pressure is contained in the well. The pushing force is necessary because the pressure inside the wellbore exerting the pipe upward. It is important because well kill operations should always be conducted when there is drill pipe inside the well bore. (Schlumberger, 2012)

Spacing out measurement of average length of drill pipe in the well to prevent the BOP close on tool joints or drill collar (Well Control School, 2004) Stand The number of joints of pipe that can be pulled and stood back at one

time by the rig, e.g., double or triples (GEKEngineering, 2010)

Stripping The process of placing drill pipe into the well bore by its own weight when the BOPs are closed and pressure is contained in the well. It is important because well kill operations should always be conducted when there is drill pipe inside the well bore. (Schlumberger, 2012) Swabbing The situation where drilling fluid tends to follow the drill string as it is

pulled from the hole causing a reduction in well/annulus (Malhotra, S., M., 2005)

Thief Zone A formation encountered during drilling into which circulating fluids can be lost (Schlumberger, 2012). Usually as a result of large open pores in the formation where sealing mud filter cake cannot be formed (Westergaard, R., H., 1987).

Transition Zone A zone where the type of flow is changing as a result of gas breakout, gas expansion, shear or turbulence (SPE E&P, 2011)

Trip Margin An amount of additional mud weight that is used to balance the reduced mud pressure in the well bore as a result of swabbing effect when performing tripping out of the hole (Malhotra, S., M., 2005)

(12)

Page | xii Trip Tank A small mud tank with a capacity of 10-15 barrels (1590–2385 liters)

usually with 1 barrel or 0.5 barrel (159 or 79.5 liters) divisions, used to make sure the required amount of mud when it is displaced by drill pipe (Malhotra, S., M., 2005)

Tripping Pulling out or replacing the drill string from the hole to change the inefficient and dulled drill bit (Schlumberger, 2012)

Tool Joint The enlarged and threaded ends of joints of drill pipe used as a pipe connection (Schlumberger, 2012)

Tool Pusher Supervisor for the drilling contractor to accommodate administration including materials, spare parts and crew’s quality assurance for efficient operations (Schlumberger, 2012)

Top Drive A pipe rotation mechanism in the travelling block section used to turns the drill string. It is suspended from the hook, so the rotary mechanism is free to travel up and down the derrick (Schlumberger, 2012)

Tubing Hanger Running Tool Tools for installation/retrieval of tubing hanger (Subsea1, 2010) Underground Blowout An uncontrollable flow of fluids from one formation into another

weaker formation through wellbore. One formation could make a kick while at the same time another formation is losing circulation (Hawker, D., 2001)

Weight on Bit The additional weight on a drill bit by adding drill collars to improve rate of penetration (Malhotra, S., M., 2005)

Wellhead The equipment used to seal and control the flow of fluids from the well that is attached on the top of the well and act as an interface between the X-mas tree/tubing hanger and the well. (Odland, J., 2010), (Subsea1, 2010)

Workover Riser A pipe connection between the drilling platform and the landing string deployed inside the marine riser to give the availability of circulate fluid, test production, well control and deployment of wireline tools (Subsea1, 2010)

Wireline Activities related to logging which employs an electrical cable to lower tools into the wellbore and to transmit data (Schlumberger, 2012) X-mas Tree A structure consists of control valves, pressure gauges and chokes

located at the top of a well where the primary function is to control the flow into or out of the well (Odland, J., 2010)

(13)

Page | xiii

ABBREVIATIONS

f feet

g gravity (specific gravity)

m Meter

psi Pounds per Square Inch AAV Annulus Access Valve AMF Automatic Mode Function AP Annular Preventer BOP Blow Out Preventer

BSEE Bureau of Safety and Environmental Enforcement DST Drill Stem Test

EDP Emergency Disconnect Package EMW Equivalent Mud Weight

ETA Event Tree Analysis FCP Final Circulating Pressure FMEA Failure Modes, Effect Analysis

FMECA Failure Modes, Effect and Criticality Analysis FTA Fault Tree Analysis

GOM Gulf of Mexico

HCR Hydraulically Controlled KT Kick Tolerance

LMRP Lower Marine Riser Package LOT Leak Off Test

LOP Leak Off Pressure LPR Lower Pipe Ram

LRP Lower Riser Package (LRP)

MAASP Maximum Allowable Annular Surface Pressure MPR Middle Pipe Ram

MTTF Mean Time To Failure MTTR Mean Time To Repair MW Mud Weight

NCS Norwegian Continental Shelf OCS Outer Continental Shelf

PLMV Production Lower Master Valve PMV Production Master Valve PUMV Production Upper Master Valve PPG Pounds Per Gallon

PWV Production Wing Valve

P&ID Piping and Instrumentation Diagram QRA Quantitative Risk Analysis

ROP Rate of Penetration

ROV Remotely Operated Vehicles

(14)

Page | xiv RPN Risk Priority Number

SCR Slow Circulating Rate SEM Subsea Electronic Module SG Specific Gravity (gm/cc) SICP Shut In Casing Pressure SIDPP Shut In Drill pipe Pressure THRT Tubing Hanger Running Tool TVD True Vertical Depth

UPR Upper Pipe Ram WOB Weight on Bit

(15)

Page | 1

1. INTRODUCTION 1.1 Background

Safety during drilling operations is the most important aspect to be considered.

Procedures, design, specifications and requirements of all aspects of drilling activities are established to make sure that the operation is safe. All companies and organizations which participate in drilling operations should perform and implement their activities to valid and approved standards and regulations. Standards and regulations vary for different geographic areas, due to many factors such as government policies, level of safety, environmental and geographical condition, etc. It should also be updated continuously to meet the specific needs and requirements which are relevant to present situation.

There are many problems that might occur during well drilling operations, particularly for subsea well drilling where remoteness and access become challenges during operations.

One of the main issues that could result in a catastrophe is the occurrence of kick (influx).

Kick is described as the unwanted influx of formation fluid into a wellbore during drilling operation as a result of pressure difference in the wellbore. This influx is unwanted because it can flow into surface and create blowout which can harm people's lives, the environment and cause property damage. The pressure inside wellbore, which is exerted by drilling fluid through drill bit, should be higher than the pressure from the formation fluid in order to make a controllable well drilling. This is known as overbalanced pressure condition. Safety precaution should be established for procedures and equipments to handle kicks and blowouts. The blowout preventer (BOP) is one of several barriers in the well to prevent kicks and blowouts and it is the most important and critical equipment as it becomes the last line of protection against blowout. The BOP is a structure with a large set of valves and rams placed on the top of the well that can be closed when the drilling crew have uncontrolled flow of formation fluid in the wellbore. If the BOP is not working properly during a kick, it will keep the well open and which can lead to a kick flow to surface and it can become a blowout.

Figure 1.1 Barrier failures in the Deepwater Macondo Accident (BP Investigation Team, 2010)

(16)

Page | 2 Figure 1.1 shows an example of how barrier failures escalated into a disaster at the Macondo Deepwater Horizon accident on 20 April 2010. In this case the last and very critical barrier, the blowout preventer, failed causing uncontrolled explosion and fire resulting in eleven losses of lives, massive oil spill, environmental damage, loss of asset and reputation as well as the impact on cost. According to the BP Investigation Team (2010) the causes of the barrier failures were not only from technical problems, but also from other factors such as human error, management and organizational issues. Some of them are related to the discrepancies of the standard and requirement for the drilling operation, particularly for BOP maintenance, procedure and operations. Therefore it is very important to identify and describe the critical components in a BOP to ensure the functionality of BOP by having the right components that should be put more focus for maintenance and testing.

1.2 Purpose

The purpose of this thesis is to determine the criticality of components in BOP related to the redundancies they have for well shut in, stripping, snubbing and BOP testing operation.

1.3 Content

This thesis describes general activities of drilling and the problems that might occur such as kicks and blowouts. The blowout preventer (BOP) as the main barriers against kicks and blowouts is the main focus in the report. Work principles, components and the use of BOP for different operations are described. The analysis of critical component in a BOP during drilling operation is discussed. To support the analysis of the criticality, some risk assessment tools are used such as reliability block diagram, failure mode effect and criticality analysis (FMECA), criticality matrix, redundancy and effect table. Standards and regulation regarding to the requirements of BOP are identified to make sure the alignment of the analysis against them.

To provide a thorough knowledge, this thesis consists of some chapters which are structured in sequence. Chapter one, gives a background, purposes, content, methodology and limitation of the thesis. Second chapter presents the general operations of drilling and how kicks can be evaluated. Kicks and blowouts as part of the problems in drilling operation are described together with its causes and indications. In order to cope with kicks problems, basic well control principles are described in chapter three. The equipments needed to control and eliminate kicks such as BOP stack and BOP control system are described in chapter four. These equipments are somehow should have redundancy in order to ensure the availability and reliability of the functions. The minimum redundancy requirements are described in chapter five including other general requirements for the design of BOP. It refers

(17)

Page | 3 to a company policy (Sedco Forex and Schlumberger) and local regulations BSEE for OCS (e.g., GOM). The use of BOP in drilling operations is described in chapter five. It includes some procedures for conducting well shut in, stripping, snubbing and testing of BOP. In order to conduct criticality analysis of blowout preventer, the suggested risk tools is presented and discussed in chapter seven. It includes reliability block diagram, FMECA, criticality ranking, criticality matrix, redundancy and effect table as the main discussion. The analysis of criticality by using the suggested risk tools is presented in chapter eight. Chapter nine present and discuss the result of criticality analysis of component in BOP as well as a discussion with regards to the use of BOP in drilling operations. Some conclusion, recommendation and suggestion for further works are presented in chapter ten. The rest of the report consists of references and appendices presented in chapter eleven and twelve.

1.4 Methodology

The methodology use in this thesis is an integrated process of guidance from supervisors, discussion with practitioners, literature study through textbooks and publications to describe drilling activity in general and to focus on the BOP by defining its function, principal, components, characteristics and operations. Relevant factors that influence the criticality of components in a BOP are described and analyzed through the literature study, aid of supervisor and practitioners. In order to analyze the criticality component of BOP, some suggested risk tools are presented and discussed. It includes reliability block diagram (RBD), failure modes, effects and criticality analysis (FMECA), criticality ranking, criticality matrix, redundancy and effect table. All of these methods are complement to each other to support the decision of the critical component in a BOP.

1.5 Limitation

This study is intended to analyze the criticality of component (barriers) in a subsea BOP. It is only focus to the components of BOP in the general stack arrangement and general control system. The analysis is conducted related to the drilling operations where the BOP is used as it gives the most contribution for the occurrence of kicks. The discussion and analysis are to some degree refers to general operations of drilling due to many variations in applications for drilling technologies, methods, government and company regulation.

Moreover, the analysis is limited to qualitative approach as there is a scarce of quantified data and the limited amount of time for the works of the report.

(18)

Page | 4

2. BASIC WELL DRILLING CONCEPT 2.1 Drilling and Completion

Drilling an oilfield is an elaborate tasks which consists of drillers, complex machineries, tools and equipments that are use to drill a well up to five to six miles below the ground to reach hydrocarbon reservoirs as efficiently and as safely as possible. All necessary equipments are mostly driven from a drilling rig which is use to lower a set of steel string carrying drill bit to make a hole and to pull it out again (Stoneley, R., 1995). Drill rigs have their own specifications and equipments needed to perform the drilling, but generally it can be as shown in the figure 2.1 below.

The drill bit is connected to the bottom of the drill string where the drill collars can be attached on it to add more weight which is necessary to give more efficient force to break rock formation. Lowering and raising these sets of drill pipes are done by means of draw-works which is connected to the travelling block. It also used to endure most of the weight of the drill string(s), drill bit and drill collar(s). The drillers should monitor the required weight of the bit to control the amount of the added weight applied.

Drill string and drill bit are both rotated by rotary table where kelly bushing are attached and connected to the drill string via kelly. The rotary table itself is driven by rig motor.

Alternatively a top drive could be used instead of rotary table. A top drive is a device that turns the drill string(s) from above where it is suspended from the hook (travelling block), so it gives free vertical movement while rotating. Kelly and kelly bushing allow connection between drill strings as the well is drilled deeper while maintaining its flexibility to rotate, raise and lower the drill string and the drill bit.

Figure 2.1 The important parts of the drilling rig (Stoneley, R., 1995)

(19)

Page | 5 Debris and cuttings of rock during drilling are carried out from the well bore into the surface by drilling fluid (mud) to be collected, examined and logged. The rock sample gives information about the formation of rock in the different depths of a well and also to give indication for the potential hydrocarbon location. Moreover, drilling fluid lubricates and cools the drill bit, balances the pressurized formation fluid that flow in the well bore and cleans out the hole. Figure 2.1 shows the flows and circulations of drilling fluid which is pumped from the mud tank into the kelly through flexible mud hose, down the hole of the drill string until it reaches and out from drill bit, goes up again to the surface carrying debris through annulus and vibrating screen to separate debris and cuttings from the mud before it end up in the mud tank again. The volume in the mud tank and the composition of mud after circulation could be a good indicator for the integrity of the well.

Protecting the wall of the hole after drilling is important to prevent it from collapsing, loss of circulation and withstand the hole from the kick. Casing is established in some depth of the well and the diameters (sizes) are varies according to the depth and formation characteristics. Generally, the deeper the depth, the less the diameters and sizes are. There are several concentric casing that would be required in the well such as conductor casing, surface casing, intermediate casing and production casing. In some depths of the well, usually where the production casing and production tubing are in place, packer would be placed in their annulus to make sure it seals completely.

Another kind of protection is blow out preventer (BOP). It is used to close and seal the well if the drilling crew loss control of formation, also known as kick and blowout. It is attached on the top of the well and consists of some types of rams that can be used for different purposes when closing a well in the emergency situation. BOP is very critical to the safety of the crew, the rig, and the wellbore itself (Subsea1, 2010).

Cementing job is important after casing has been placed in order to prevent the loss of drilling fluid and to seal the annulus between casing and well bore by filling it with proper cement so there is no spaces in the annulus. Primary cementing is placed right after the casing has been run into the hole and if deficiency occurs, then secondary cementing might be done. Casing and cementing operations are parts of the well completion during drilling operation. Drilling and completion operations usually are in line as they are acted as complement to each other to make a good well integrity.

Offshore drilling operations have quite similarities with the onshore drilling as mentioned above. There are some differences in the equipments used particularly during completion as it is drilled from the seabed. Marine riser, work over riser, lower marine riser package (LMRP), lower riser package (LRP), emergency disconnect package (EDP), landing string and tubing hanger running tool (THRT) might be used. There are many different systems and approaches that can be used, but the most common systems are landing string

(20)

Page | 6 systems for running in marine riser, simplified landing string systems for running in marine riser, open water systems with workover risers and riserless open water system (Subsea1, 2010).

Figure 2.2 shows the example of completion by using landing string systems for running in marine riser.

The number of components can be listed as follows (Subsea1, 2010) : 1. Surface Flow Tree

2. Rig

3. Marine riser 4. Workover riser 5. LMRP

6. Landing string 7. BOP

8. THRT

9. Tubing hanger & X-mass tree 10. Wellhead

11. Completion/tubing 12. Well

The offshore drilling can be done from fixed structures (e.g.

jacket platform, gravity based platform, etc) or floating structures (e.g. semisubmersible platform). To secure the position of drilling on the seabed, subsea drilling template might be used. Blow out preventer and X-mass tree could be installed on the platform (surface/dry tree) for fixed platform or on the sea bed (subsea/wet tree) for floating platform where the well head is attached on the seabed.

Figure 2.2 Completion by using landing string systems for running in marine riser (Subsea1, 2010)

Figure 2.3 Surface and Subsea Tree (Odland, J., 2010)

(21)

Page | 7 The tree is installed by replacing (removing) BOP during completion operation when drilling is finished and the well is ready for production. To start production, perforation is conducted by making a hole in the casing and formation. The hole in the formation will make a differential pressure which allows the hydrocarbon to flow from high pressure reservoir into the lower pressure of well and up to the surface. The flow of the fluid is control by the tree.

The design, installation, operation and maintenance for surface trees are simpler than for wet tree.

The design of well construction is different from one area to other area, it depends on the location (depth) of the reservoir, layers of rocks that should be drilled, drilling fluid, pressure, temperature, integrity, fracture strength, hole stability of the formation, the available equipment, the economic operation and most importantly the safety of personnel. Here is an example of typical well construction in the North Sea (Odland, J., 2010), (Serene Energy, 2010):

1. Drill 30” – 36” hole to approximately 120 m below seabed by using sea water as a drilling fluid. To place the conductor, it can also be done by using piling technique.

2. Set conductor of 30” diameter.

3. Drill 26” surface hole to approximately 500 m by using mud as a drilling fluid.

4. Run and set 20” surface casing.

5. Cement surface casing and wellhead housing is installed on the top of the casing to provide the weight support of the casings that will be installed after. The BOP is also installed on the top of the casing to anticipate the possibility of high pressure formation fluid that might contain in the next drilling phase.

6. Drill 17½ “ intermediate hole to approximately 1800 m.

7. Run and set intermediate casing (13 3/8”).

8. Cement intermediate casing.

9. Drill 12 1/4” hole to top of reservoir. In this dept there would be a possibility of hydrocarbon presence in the formation and the sample of drill cutting are collected and examined. The formation in the well is also examined by using wireline technique to know the porosity of the rocks, shale and sands. Drill stem test can also be performed here after knowing the possibility of potential hydrocarbon and the formation fluid that flows in the well.

10. Run and set production casing (9 5/8”) 11. Cement casing.

12. Drill 8 ½” hole.

13. Run, set production tubing (7”) and placed packer in the annulus between production casing and production tubing

14. Remove BOP and replace with Xmass tree 15. Perforate and production

(22)

Page | 8

2.2 Kicks and Blowouts

During drilling operations many problems that can occur such as casing collapse, casing burst, kick, blow out, leaking tube, gas filled casing, etc. Kick and blow out could result in the most catastrophe event in the term of costs, assets, environmental damage and personnel safety when its occurrences and escalations are not handled properly. A kick should be detected early before it reached surface and become a blow out. The crew who work with drilling activities should understand the behaviors and characteristics related to the kick as well as the principles, the causes, the warning signs and the indicators. Drilling and tripping activities are contributing the most for the kick event to occur. In addition, it is also very important to comprehend the theories and procedures for well control operations.

The causes of kicks and blowouts are principally a result of pressure difference in the annulus between the wellbore and the formation. The pressures that are exerted from the drilling fluid should balance the pressure from the formation fluid. It should be larger than the pressure of fluid from the formation. However, the drilling fluid pressure could not be larger than the fracture pressure in the formation which can cause a formation fracture. When fracture occurs, there will be a diversion flow of drilling fluid (mud) into the fracture area resulting in a loss of mud circulation which reduces hydrostatic pressure in the annulus allowing formation fluid to flow up through the annulus and possibly to the surface. Moreover, the fractured formation allows high pressure fluid to flow inside it and if the formation is weak the flows could break the weaker formation above and reach the surface on any random location known as cratered blowout. The blowout will make well control operations become harder.

Kick is occur when the pressure of drilling fluid (mud) in the wellbore has less pressure than the pressure flows in the formation fluid, whether as a result of the loss of mud circulation or increase pressure in the deeper formation, making an unwanted influx of formation fluid into the wellbore. A blowout (surface blowout) occur when an uncontrolled kick in the wellbore reaches the surface, endanger the safety of rig, personnel and environment. Underground blowout occurs when the uncontrolled flow of formations is flowing into another weaker formation.

Figure 2.4 Underground blowouts from a well reach surface (Chu, D., L., 2010)